The present invention relates to a writing instrument with automatic advancement of a lead and feeding of successive leads.
Writing instruments of the above-mentioned general type are known in the art. A known writing instrument has a spring-biassed writing pipe actuated by the lead advancement and connected with a lead receiving device, and a clamping member with several clamping arms which is longitudinally movable for closing and opening and abuts under the action of a spring against a gripping sleeve, wherein its clamping opening communicates with an inlet funnel facing toward the lead container. In lead writing instruments with automatic advancement of solid leads actuated by the writing pressure and released by lifting of the instrument from the substrate, a free passage from the lead container to a brake element connected with the writing pipe must be guaranteed so as to provide that without additional actuation of an adjustment member, leads can be automatically transported one after the other from the lead container through the clamping opening of the clamping member to the front end of the lead protecting pipe. During writing and wearing of the lead, it must be continuously supported against the writing pressure and, immediately after lifting of the lead protecting pipe from the object to write on, transportation of the lead synchroneously with the lead protecting pipe must be carried out. The length of the lead to be transported must have no influence upon the intended functions.
One of such writing instruments is disclosed, for example, in the German Offenlegungsschrift No. 2,837,586. In the instrument described in this reference both the lead can be automatically transported forwardly, and a free passage from the lead magazine to the braking member on the lead protecting pipe is provided. For this purpose, after each lifting of the tip of the instrument from the object, the lead moves forwardly through the carrying element and the clamping member is simultaneously opened so wide that a subsequent lead can move from the lead container through the clamping opening of the clamping member. The axial movement relative to the gripping sleeve required for opening of the clamping member is actuated by a coupling which engages in the counter member via a control edge. In order to provide for a coupling, a certain minimal stroke of the lift protecting pipe and the connected coupling member must be first carried out to reach the control edge which releases the coupling process. During such a movement process, it can happen that in the event of frequent short lines the lead automatically moves forwardly and thereby a lead transportation takes place. The clamping member is not opened but frictionally abuts against the lead so that a lead cannot fall from the lead container through the clamping opening of the clamping member and can be engaged by the elastic carrying element.